Rotary electric transformers for tube welding



ROTARY ELECTRIC TRANSFORMERS FOR TUBE WELDING Filed Nov. 27, 1965 H. O. BRADSHAW Sept. 6, 1966 5 Sheets-Sheet 1 Haw-T Oslaakwi B vac] 3144M,

ROTARY ELECTRIC TRANSFORMERS FOR TUBE WELDING Filed Nov. 27, 1963 Sept. 6, 1966 H. o. BRADSHAW 5 Sheets-Sheet 2 HQVFY O born e Brucjsh/aw p 6, 1956' H. o. BRADSHAW 3,2

ROTARY ELECTRIC TRANSFORMERS FOR TUBE WELDING Filed Nov. 27, 1963 5 Sheets-Sheet 3 J -LLL Z a z 1' Harry Osbome Bradskavw United States Patent 3,271,712 ROTARY ELECTRIC TRANSFORMERS FOR TUBE WELDING Harry Osborne Bradshaw, Birmingham, England, assignor to Tube Products Limited, Birmingham, England, a British company Filed Nov. 27, 1963, Ser. No. 326,451 Claims priority, application Great Britain, Nov. 27, 1962, 44,7 6 1/ 62 2 Claims. (Cl. 336-82) This invention relates to improvements in rotary electric transformers of the kind used for the continuous welding of tubes.

One known type of rotary transformer use-d for tube welding comprises a hollow single turn secondary enclosing a multi-turn primary wound on an annular core. The current from this secondary turn has to be applied to a pair of axially offset circular electrodes for engagement with the surface of the tube to be welded. Conductors conveying the welding current from the secondary to the electrodes are taken through a throat of reduced diameter which is mounted in a bearing taking the mechanical load.

Various arrangements have been proposed for these conductors, including concentric tubes reduced in diameter from the transformer secondary so that they may be passed through the mechanical bearing. These conductors are required to carry very heavy currents and at the same time to have a low ohmic resistance and inductive reactance, and determine the overall efficiency of the welding transformer.

The purpose of my invention is to provide a system of conductors having a low ohmic resistance together with a low inductive reactance so that the overall efiiciency of the transformer is improved.

According to my invention, in a rotary transformer of the kind set forth above, current is conveyed from the secondary to the electrodes through the throat of the transformer by concentric sleeves formed with co-operating complementary inteleaved or interpenetrating longitudinally extending corrugations, flutes or ribs of which the surfaces are substantially parallel but are spaced a short distance from each other.

One example of a transformer embodying my invention is illustrated in the accompanying drawings in which:

FIGURE 1 is a side elevation of the transformer in longitudinal section above the centre line;

FIGURE 2 is a side elevation of the outer conductor sleeve in longitudinal section above the centre line;

FIGURE 3 is an end view of the outer conductor sleeve half in section on the line 3-3 of FIGURE 2;

FIGURE 4 is a side elevation of the inner conductor sleeve in longitudinal section above the centre line; and

FIGURE 5 is a fragmentary section through the assembled conductor sleeves.

In the transformer illustrated, a single turn secondary is mounted on and insulated from a rotatable shaft 11. The primary winding (not shown) which is wound on a core 12, is fed with current from slip rings 13, 14 in the usual manner. The output current from the secondary is fed through a throat 15 of reduced diameter to two circular electrodes 16, 17 which engage with the surface of a tube to be welded adjacent to the weld point. The throat 15 is mounted in a roller bearing 18 in a fixed housing 19, the bearing taking the mechanical load on the electrodes.

The secondary has a gap 21 on its inner side at the end adjacent to the electrodes and is connected on opposite sides of the gap to the electrodes by two concentric sleeves 22, 23. The outer sleeve 22, shown separately in FIG- URES 2 and 3, is formed with a series of angularly spaced deep longitudinal ribs 24 extending radially inwards and having their side faces inclined at such angles as to leave between the ribs parallel-sided longitudinal slots or gaps 25.

The inner sleeve 23, shown separately in FIGURE 4, is formed with a series of parallel-sided ribs 26 projecting radially outwards and spaced angularly at the same spacing as the ribs 24 on the outer sleeve.

The relative dimensions of the ribs and intervening gaps on the two sleeves are such that when the sleeves are assembled together, as shown in section in FIGURE 5, the ribs on one sleeve enter between those on the other sleeve and the faces of the ribs on the two sleeves are parallel or substantially parallel to each other. Suflic-ient clearance is provided between the ribs for the passage of oil for cooling.

The sleeves are located in accurate concentricity by their engagement at one end with the secondary and at the other end with means for clamping them axially on the shaft.

The co-operating ribs or flutes on the conductor sleeves provide a large surface area for the flow of current so that the current density is reduced to a relatively low value and losses are reduced to a minimum. Additionally the close proximity of the two concentric conductors in combination with the ribbed or fluted arrangement produces a conductor system having low inductive reactance.

This is important in that the k.v.a. rating of the alternator feeding the transformer can be reduced as compared with that necessary for the supply of welding current to a transformer having higher inductive reactance values.

Other advantages of my improved transformer are that it contains a minimum number of parts, is easy to assemble, and dismantle, and that the throat has high mechanical rigidity.

I claim:

1. A rotary transformer incorporating a single-turn secondary connected electrically to axially offset circular electrodes by conductors passing through a throat of reduced diameter mounted in a bearing, wherein said conductors comprise concentric inner and outer sleeves, longitudinally extending angularly spaced portions on the inner sleeve extending outwardly therefrom, and complementary longitudinally extending a'ngularly space-d portions on the outer sleeve extending inwardly therefrom, said portions on the two sleeves being interengaged when the sleeves are in assembled relationship and the adjacent surfaces of said portions being substantially parallel and spaced from each other.

2. A rotary transformer incorporating a single-turn secondary connected electrically to axially offset circular electrodes by conductors passing through a throat of reduced diameter mounted in a bearing, wherein said conductors comprise concentric inner and outer sleeves, angularly spaced deep longitudinal ribs projecting radially outwards from said inner sleeve, and complementary angularly spaced deep longitudinal ribs projecting radially inwards from said outer sleeve, the rib-s on each sleeve entering between the ribs on the other sleeve when the sleeves are assembled together and the adjacent surfaces of the ribs being substantially parallel and spaced from each other.

References Cited by the Examiner UNITED STATES PATENTS 2,605,376 7/1952 Schuttler 336223 X 2,969,421 1/1961 Scott 174-133 X 3,130,290 4/1964 Keska 21963 4 FOREIGN PATENTS 1,000,543 1/1957 Germany.

LEWIS H. MYERS, Primary Examiner.

ROBERT K. SCHAEFER, Examiner.

T. J. KOZMA, Assistant Examiner. 

1. A ROTARY TRANSFORMER INCORPORATING A SINGLE-TURN SECONDARY CONNECTED ELECTRICALLY TO AXIALLY OFFSET CIRCULAR ELECTRODES BY CONDUCTORS PASSING THROUGH A THROAT OF REDUCED DIAMETER MOUNTED IN A BEARING, WHEREIN SAID CONDUCTORS COMPRISING CONCENTRIC INNER AND OUTER SLEEVES, LONGITUDINALLY EXTENDING ANGULARLY SPACED PORTIONS ON THE INNER SLEEVE EXTENDING OUTWARDLY THEREFROM, AND COMPLEMENTARY LONGITUDINALLY EXTENDING ANGULARLY SPACED PORTIONS ON THE 